A mechanical ventilator delivers air to a patient via tubing called a breathing circuit, and in some cases mixes additional oxygen into the air before being delivered to the patient. The gas delivered to the patient from the ventilator may be humidified and heated in the breathing circuit before it goes to the patient. The ventilator increases the pressure in the breathing circuit so that the air is pushed into the lungs for inspiration, and reduces the pressure so that the air in the lungs can be expired and vented to the atmosphere. Typically, one or more ventilator parameters may be determined and adjusted prior to attachment and during operation on the patient, including the mode of ventilation (e.g., CMV (controlled mandatory ventilation), SIMV (synchronized intermittent mandatory ventilation), or CPAP (constant positive airway pressure)); the patient's tidal volume (the volume of air inspired with each breath); the respiratory rate (the number of breaths per minute (BPM)); and the O2 concentration, flow rate, airway pressure, and minute volume (the volume inspired and expired in one minute) of gas delivered to the patient.
Some ventilators generate noise during operation, which may be undesirable to the ventilator user or operator, particularly when the user is trying to sleep. For example, some breathing assistance systems include motors or other components that may produce a continuous noise, such as a humming, buzzing, or whining. In addition, the flow of air though a ventilator, particularly at high speed or high pressures, may produce undesirable noise.